Not applicable
1. Field of the Invention
This invention relates to molten metal pumps such as are used in, but not restricted to, aluminum facilities.
2. Background Information
Prior art molten metal pumps are described in patents including:
Molten metal pumps are used for circulating, transfering, and gas injecting molten metal. It is a harsh environment so the pumps have relatively short lives and are expensive to repair. The pumps are difficult to disassemble. The supports are difficult to remove from bases as they typically are cemented in place.
Pumps with impellers of a nine inch or greater diameter currently use 25 horsepower, or larger, direct drive electric motors with expensive variable frequency drive units.
Motor mounts tend to warp after exposure to heat from the molten metal. Insulation used below the motor mounts tend to get torn off with normal production use. As a motor mount warps, pump alignment is affected and tends to cause a rotating shaft to lock up. Also, warping of the motor mount puts added stress on a pump base, and tends to cause the base to crack, which destoys the pump.
After existing pumps are in use, it is difficult to get a used shaft uncoupled from its pump.
Some existing pumps use a ceramic bearing below the surface of molten metal. The ceramic bearing is susceptable to thermal shock and prone to failure. Other existing pumps do not use a ceramic bearing, and there are problems with motor bearings and couplings.
There are problem areas in how supports are joined to pumps in that alignment is a problem. Also, cement is relied on, in some cases, which requires a drying times that, combined with painstaking procedures typically required a two day repair cycle.
Existing pump bases are typically a monolithic block that does not lend itself to repair.
Existing pump impellers have problems. Impellers with cup shapes tend to clog up. Exisitng vane impellers have edges that wear away rather rapidly, so efficiency is lost. If the pump speed is increased, to compensate for the loss in efficiency, dross is created by the higher speed. Existing vane and cup impellers are made out of a monolithic block and machined so they have to be threaded to a shaft, or cemented and pinned to a shaft. That means not all the vane area is utilized for pushing metal but is used to adhere to the shaft. The monolithic block construction results in internal cavity shapes that are not optimum from a performance standpoint due to geometric limitations of what can be accomplished by a machine tool in machining an impeller from a block.
Also, the pump impeller housings are machined from a block. This could be called a monolithic block construction. Carbon graphite is anisotropic in nature. This means it has different strengths in different directions. This is a limiting factor in the structural strength of prior art pump impeller housings.
As will be seen from the subsequent description, the preferred embodiments of the present invention overcome these and other shortcomings of exisitng liquid transport apparatuses.
The present invention is a chambered vane impeller molten metal pump comprising a drive means, a motor mount with improved gussets, a coupling with a taper for easy shaft removal, a shaft with a tapered top and a bottom with dovetail mating grooves for accepting impeller vanes, a journal bearing above or below a mount for the drive means, tapered Dost sockets, supports each with an end tapered and the other end grooved, support sheaths, a laminated base, a fabricated chambered vane impeller, and an outlet.
In the preferred embodiment of the present invention, the drive means is an electric motor and a gear box with a soft start package so as to control initial start up accelerations. An alternate embodiment is an air motor and gear box combination. Another alternate embodiment is a hydraulic drive motor.